Pneumoviruses are a group of viruses that infect the respiratory system. The name itself offers a clue, with “pneumo” being a Greek term for the lungs. These viruses belong to the Pneumoviridae family and are categorized as negative-strand RNA viruses. This genetic makeup dictates how they replicate within a host’s cells.
These pathogens are responsible for a significant number of respiratory tract infections in humans, as well as in other animals. Their structure is pleomorphic, meaning they can appear as both spherical and filamentous particles. The viral particles are enveloped, which means they are surrounded by a fatty membrane, and measure between 150 to 200 nanometers in diameter.
Common Types of Human Pneumoviruses
Two main types of pneumoviruses are known to cause widespread illness in humans: Human Respiratory Syncytial Virus (RSV) and Human Metapneumovirus (hMPV). Both are significant causes of lower respiratory infections, particularly in young children. RSV is particularly pervasive, with estimates suggesting that nearly all children will be infected with the virus at least once by the time they are two years old.
RSV infections follow a seasonal pattern, emerging as an annual epidemic during the winter months in temperate climates. This virus poses the greatest risk to infants under six months of age, the elderly, and individuals with compromised immune systems, for whom it can lead to severe lower respiratory tract diseases. The global impact of RSV is substantial, causing up to 200,000 deaths annually worldwide.
Human Metapneumovirus (hMPV), first identified in 2001, is the second most common cause of lower respiratory infections in young children. Its discovery highlighted that not all severe respiratory illnesses were attributable to RSV. Like RSV, hMPV infections are most common during the winter and early spring, and the at-risk populations are very similar.
Symptoms and Transmission
Pneumovirus infections can produce a wide spectrum of symptoms, ranging from mild to severe. In many healthy adults and older children, the illness resembles a common cold, with symptoms such as a runny nose, a persistent cough, and a low-grade fever. These initial signs appear within four to six days after exposure to the virus.
The severity of the illness depends on the individual’s age and underlying health conditions. In more vulnerable populations, the infection can progress from the upper to the lower respiratory tract. This can lead to serious conditions like bronchiolitis, an inflammation of the small airways in the lungs, and pneumonia. Symptoms of a severe infection include wheezing, rapid breathing, and a bluish tint to the lips or fingers, indicating a lack of oxygen.
Transmission of pneumoviruses occurs through respiratory droplets. When an infected person coughs or sneezes, they release virus-containing droplets into the air, which can then be inhaled. The viruses can also be spread through direct contact or by touching contaminated surfaces and then touching one’s face. This makes settings like daycares and nursing homes common locations for outbreaks.
Diagnosis and Management
Diagnosing a pneumovirus infection begins with a clinical evaluation. A doctor will consider the patient’s symptoms and the time of year, as infections are more common during specific seasons. For many mild cases, a specific diagnosis is not pursued. However, for more severe cases, laboratory tests can be performed, which involve a nasal swab or aspirate to collect a sample for analysis.
Since these are viral infections, antibiotics are ineffective, and treatment focuses on supportive care to manage symptoms. For mild illness, this includes ensuring adequate hydration, getting rest, and using over-the-counter fever reducers and pain relievers. Most people with mild infections recover within one to two weeks.
In cases of severe respiratory distress, hospitalization may be required. Hospital-based care can include oxygen support to help with breathing and intravenous fluids to prevent dehydration. Prevention is an important strategy, with frequent handwashing being an effective measure. For high-risk infants, preventative antibody treatments are available, and vaccines have been developed for older adults to protect against severe RSV.